Comparison of the adsorption kinetics of methylene blue using rice husk ash activated with different chemical agents

Activated carbon is widely used in several industrial sectors and has a high production cost. To reduce costs, different materials have been studied, for example, rice husks (RH). RH is an abundant, low-cost residue of the agricultural sector and can be used to generate energy due to its high calorific value. However, burning husk generates waste, the ashes. Thus, the objective of this work was to optimize the synthesis of activated carbon using pre-carbonized RH with different chemical agents as activators (KOH, NaOH, NaCl, H₂SO₄, and Na₂CO₃), at different particle sizes. Subsequently, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) were used to characterize the materials. Of these, KOH was the best activating agent. The adsorption kinetics for the adsorbents was 30 min, reaching equilibrium after 70 min. Of the three fitted kinetic models, pseudo-second-order and Elovich best fit the data. The FT-IR shows that the adsorbents have oxygenated surface groups such as alcohol, ester, ether, and phenol. From the point of zero charge, the predominance of negative charges on the surface of the adsorbents is observed. Therefore, the activated carbon from rice husk ash (RHA) showed potential in the adsorption of the methylene blue dyes.